1. Field of the Invention
The present invention relates to a technique in which a localization is performed in a vehicle such as an autonomous mobile vehicle or a logistics support robot using a combination of a plurality of localization methods.
2. Description of the Related Art
It has been known that a combination of a plurality of localization methods such as GPS (Global Positioning System) and various landmarks is effective for performing a localization, that is, a self-position estimation, with high accuracy and improved reliability in a vehicle (a movable body with or without a human or an object mounted thereon) such as an automobile or a robot, as disclosed in Japanese Laid-Open Patent Application, Publication No. 2004-219332, “Vehicle, p142-p173 (K. Kanai et al; Corona Publishing Co., Ltd. (2003))”, and “Probabilistic Robotics, p121-p166 (S. Thrun, W. Burgard, and D. Fox; MIT Press (2005))”. In performing the localization, it has also been known that effective localization methods are different according to target travel environments, and thus, a combination of localization methods suitable for a given travel environment has to be determined in some appropriate way.
Japanese Laid-Open Patent Application, Publication No. 2004-163424 discloses a technique in which, in performing a localization not using a combination of localization methods but using GPS alone, a localization accuracy in a target travel environment is simulated.
Note that the above-mentioned localization using various landmarks means a localization using, as a reference, a stationary body which is available as a marker (that is, a landmark) present in a travel environment and whose position has already been known, such as a tree, a utility pole, and a building wall. The localization using GPS is, in other words, a localization using GPS satellites as landmarks.
There has been a problem of how a suitable combination of localization methods in a travel environment can be selected. The above-mentioned related art documents describe in detail a technique of a position estimation in a case where a suitable combination of localization methods is previously known. However, the related art documents do not disclose how to determine a suitable localization method combination. Further, the related art documents do describe a technique which enables a localization accuracy prediction if GPS is used, but do not disclose a technique which realizes a localization accuracy prediction if a combination of a plurality of localization methods is used.
A determining system for localization methods combination according to the related art is usually performed as follows. A tentative combination of localization methods is determined. The determining system of the tentative combination is mounted on a vehicle. A test using the vehicle and other actual equipment is conducted in a target travel environment. A localization accuracy of the tentatively-determined combination of localization methods cannot be evaluated until completion of the test. If the localization accuracy of the combination subjected to the test cannot achieve a target localization accuracy, it is necessary to start such a process again from determining another tentative combination of localization methods. This presents a problem that it takes much time and cost.
In light of the problems as described above, the present invention has been made in an attempt to determine a combination of localization methods which can achieve a target localization accuracy at low cost.
If a localization accuracy of each localization method in a target travel environment is previously predictable, a suitable combination of localization methods which can achieve a target localization accuracy at low cost can be determined without conducting a test using actual equipment. However, a localization accuracy of a localization method varies according to travel environments, which makes it difficult to know the localization accuracy in advance. In the related art, the localization accuracy is known only after a vehicle with the localization methods mounted thereon is built and actually performs a localization in the travel environment. The present invention is in an attempt to solve the problems based on the following findings obtained by the present inventors.
According to the findings of the present inventors, a localization accuracy of a localization method depends on a layout of landmarks used by the localization method or a landmark position detection accuracy, which can be represented as a numerical parameter. The parameter can be examined even without conducting any localization using actual equipment. Further, a relation between the parameter and the localization accuracy of the localization method can be maintained to build a database. By referencing the database, the localization accuracy of the localization method in the target travel environment can be predicted without conducting an actual localization. Consequently, based on the predicted localization accuracy of the localization method, a combination of localization methods suitable for achieving a target localization accuracy can be determined.